Read time: 10 minutes

Target audience: Thermal Researchers/ EV Automobile Engineers/ Thermal-Fluid Industry/ Aero Industry
Written by: Dr. Tabish Wahidi

1. Background The article discusses RapidFlow, a specialized fluid-flow solver designed to accelerate thermal-fluid simulations, particularly for vehicle cabins. It is tightly integrated with the TAITherm thermal simulation platform, offering a faster alternative to traditional CFD (computational fluid dynamics) coupling while retaining fluid modeling fidelity. Typical cabin airflow and thermal comfort simulations that might take days with full TAITherm-CFD coupling can be performed much more quickly with RapidFlow without sacrificing essential accuracy.
2. Introduction RapidFlow is introduced as a high-speed transient fluid solver optimized for thermal simulations and integrated directly into the TAITherm environment. Its purpose is to enable engineers to analyze airflow and convective heat transfer more efficiently than conventional CFD approaches, striking a balance between computational speed and result accuracy. Benchmark comparisons show the solver can reduce total simulation time by about an order of magnitude compared to the traditional TAITherm-CFD coupling approach.
3. Methodology RapidFlow within a TAITherm project involves a few key steps: • Fluid Domain Setup: Users begin by creating a new fluid part and enabling RapidFlow within that part, making sure it is positioned properly inside the fluid domain of the model. • Surface Connections: Relevant surfaces are linked to this fluid part using convection settings to allow RapidFlow to compute convective interactions. • Solver Configuration: Outside of the TAITherm interface, simulation parameters and fluid conditions for RapidFlow are defined in a text-based configuration file provided with the software distribution. Users then simulate the GUI, command line, or via scripting/automation tools. • Result Visualization: After the run, thermal surface results are viewed in TAITherm, while detailed fluid flow fields can be examined using visualization applications like ParaView. In addition, RapidFlow’s integration enables coupling with 1-D tools and system models such as GT-SUITE. In such setups, GT-SUITE handles system-level HVAC controls, RapidFlow computes the airflow and convection within the cabin, and TAITherm manages conduction, radiation, and occupant physiology, allowing feedback between the solvers for advanced control law evaluation.
4. Case Study The article highlights a benchmarking comparison between a traditional TAITherm-CFD coupling and the TAITherm-RapidFlow combination for a 30-minute transient cabin cooldown scenario: Method Total Run Time Fluid Solve Time Avg. Surface Temp Error (°C) Avg. Air Temp Error (°C) TAITherm-CFD Coupling 34.9 hr 15.8 hr 0.67 –0.99 TAITherm-RapidFlow 1.9 hr 0.4 hr 0.94 –2.29

This shows that while RapidFlow runs significantly faster (around ten times less total computation), the differences in predicted temperatures remain relatively small, demonstrating the solver’s practical efficiency for transient thermal analyses.
Integration with 1D System Modeling Tools
Because RapidFlow is fully embedded within TAITherm, it supports the same advanced co-simulation functionality available with the standard solver. A thermal model incorporating RapidFlow can be linked with 1D system simulation platforms, enabling fast automotive HVAC analysis, advanced controller development, control strategy optimization, and related studies.

For instance, a streamlined workflow can connect TAITherm and RapidFlow with Gamma Technologies’ GT-SUITE to evaluate passenger thermal comfort, cabin temperature distribution, and HVAC power consumption within a vehicle interior. In this integrated setup, each tool performs a distinct role:
• GT-SUITE: Computes HVAC operating conditions using a user-defined PID control algorithm and periodically transfers those system inputs to RapidFlow.
• RapidFlow: Simulates the internal airflow field and convective heat transfer using HVAC inputs from GT-SUITE along with the geometric data from the TAITherm model. It then transfers the calculated convection information from cabin surfaces and occupants back to TAITherm.
• TAITherm: Handles conductive and radiative heat transfer, as well as environmental effects such as solar loading and wind conditions. It also models human thermophysiology to determine occupant thermal response. Using the convection data received from RapidFlow, TAITherm computes surface temperatures and physiological metrics, and then feeds the occupant comfort results back to GT-SUITE for use in the PID controller logic.

1. Conclusion: In summary, RapidFlow is presented as a powerful, efficient solver that enhances TAITherm’s capability for thermal-fluid cabin simulations. By significantly cutting down simulation time while preserving fluid modeling accuracy, it enables quicker design iterations, early-stage exploration, and easier inclusion of complex airflow effects than traditional CFD coupling approaches. Its full integration also supports co-simulation with system-level tools for advanced HVAC and comfort analyses, making it a valuable tool in automotive thermal simulation workflows.